Electrically excited lasers are known from German Patents 2 608 830 and 2 735 299. Herein, the discharge space is enclosed between the wall surfaces of a waveguide. These wall surfaces of the waveguide are circumferential surfaces of two concentric cylinders. The waveguide extends lengthwise in the direction of a cylinder axis and so mirrors of a resonator are arranged at both end faces of the cylindrical waveguide.
Such a waveguide configuration has the disadvantage that, as a rule, a number of optically incoherent laser regions occur which, in particular, are uncoupled from one another transversely to the optical axis, i.e., in the azimuthal direction, so a single laser mode, as required for expedient use of such a laser, is not available. On the other hand, with such high-frequency-excited, diffusion-cooled gas lasers, possibilities are always being sought for making the waveguide wall surfaces as large as possible in order to have a discharge space volume which is as large as possible, as there are only slight variation possibilities as far as the spacing between the waveguide wall surfaces is concerned.
Enlargement of the waveguide surfaces in all conceivable directions, which, in principle, is possible, also creates problems, as either radiation can occur transversely to the lengthwise extent of the waveguide, resulting in undesired losses, or the waveguide configuration becomes very long and is, therefore, hard to handle in practical application.